PTHrP was discovered in the late 1980s as the mediator of the syndrome of humoral hypercalcemia of malignancy, and it was at that time a molecule in search of a function. One PTHrP function is as a developmental regulatory molecule. The best defined such effects are in endochondral bone formation, the eruption of teeth, and formation of the mammary epithelium. In adults, PTHrP functions as a mechanically-induced product in smooth muscle structures throughout the organism. For the past several years, our group has focused on PTHrP in other excitable cells, and we propose here four projects to further our understanding of these potential functions. Two of these projects (3 and 4) are entirely new initiatives. Aim 1 is to create a lacZ PTHrP knock-in by homologous recombination. This project is at the blastocyst-injection stage. This allele will provide a PTHrP gene readout in physiological regulation and in conditional deletion experiments. Aim 2 is to create models that will enable study of the potential role of PTHrP as a neuroprotective peptide. One subaim will be to conditionally delete PTHrP from a CA3 subfield of the hippocampus via a kainite receptor-driven Cre and a second subaim to delete PTHrP from the CA1 subfield by an inducible calmodulin kinase-driven Cre. Subaim 3 is create models that will enable study of PTHrP involvement in neuronal regeneration, based on preliminary evidence in vitro that suggests such a function. One subaim will be to delete PTHrP in peptidergic primary sensory neurons of the dorsal root ganglia and a second to delete PTHrP in epidermal structures via an inducible Cre-targeting system. These models will focus on potential PTHrP functions in DRG and cutaneous nerve regeneration, respectively. Aim 4 will focus on the potential role of PTHrP in mechanical-regulated bone formation in vivo. This aim too is based on preliminary evidence of such an effect in vitro. The model to be created will be a collagen gene-driven Cre under the control of PR1 (RU-486).